in common parlance refers to the
emission of visible light from
a substance being irradiated by
ultraviolet light, which the human
eye cannot see. Some minerals,
for example, fluoresce in the
infrared, but we cannot see the
emitted light. Moreover, the agent
that causes a given substance
to fluoresce need not be ultraviolet
light-it could just as well be
an electron beam, or X-rays, or
even visible light of a different
wavelength from that emitted.
All fluorescence, however, involves
the addition of energy by some
means to a substance, and the
reemission of part of that energy
as electromagnetic radiation.
color change phenomena is a result
of the presence of trace amounts
of vanadium and chromium +3 ions.
These trace elements apparently
effect the absorbtion bands of
the mineral. When the light has
a greater amount of ultraviolet(daylight),
the stone will be blue or green,
but when the light source is reddish
(incandescent), the stone appears
red, purple or raspberry.
is caused when needle-like inclusions
orient themselves perpendicular
to a crystal face. In sapphire
and ruby, a hexagonal crystal,
the star will appear 6 sided.
In diopside, an orthorhombic crystal,
the star appear 4 sided.
effect seen on certain minerals
which causes it to display a billowy,
rounded, ghost-like reflection
with a bluish-whitish color emanating
from the surface when the mineral
is cut into a cabochon. It is
caused by structural anomalies
or build up of water in the mineral.
The minerals most famous for exhibitingadularescence
are Opal and Moonstone. The name
is derived from Adularia,
of which Moonstone is a variety
needlelike inclusions of microscopic
that reflect a streak of light
as in Tiger's eye, Pietersite,
& Charoite. A chatoyant stone
with just a slight change in viewing
angle changes it from light to
is a remarkable property of certain
minerals to temporarily change
Very few minerals exhibit tenebrescence,
also known as reversible photochromism,
but at least two do, hackmanite,
a variety of sodalite, and tugtupite.
behavior is exploited in synthetic
materials for the manufacture
of self-adjusting sunglasses,
which darken on exposure to sunlight.